Genetically predisposed individuals, who make up about 10% of the population, become hypersensitized (allergic) to antigens from a variety of environmental sources to which they are exposed. Those antigens that can induce immediate and/or delayed types of hypersensitivity in people are called allergens. King, T. P., Adv. Immun., 23:77-105 (1976). The symptoms of hay fever, asthma and hives are forms of allergy which can be caused by a variety of allergens, such as products of grasses, trees, weeds, animal dander, insects, food, drugs and chemicals. The antibodies involved in allergy belong primarily to the immunoglobulin E (IgE) class of immunoglobulins. IgE binds to mast cells and basophils. Upon combination of a specific allergen with IgE bound to mast cells, the IgE is cross-linked on the cell surface, resulting in the physiological effects of IgE-antigen interaction. Degranulation results in release mediators including histamine, heparin, a chemotactic factor for eosinophilic leukocytes and the leukotrienes, C4, D4 and E4, which cause prolonged constriction of bronchial smooth muscle cells. Hood, L. E. et al., Immunology, (2nd ed.), pp 460-462, The Benjamin/Cumming Publishing Co., Inc. (1984). The effects of allergen on an individual may be systemic or local in nature, depending on the route by which the allergen entered the body and the pattern of deposition of IgE and mast cells. Local manifestations generally occur on epithelial surfaces at the location at which the allergen entered the body. Systemic effects can include anaphylaxis (anaphylactic shock), which is the result of an IgE-basophil response to circulating (intravascular) allergen.
It has been estimated that there are approximately 10 million cat allergic individuals in the United States. Ohman, J. L., and Sundin, B., Clin. Rev. Allergy, 5:37-47 (1987). An allergen of particular concern for many people is the feline skin and salivary gland allergen of the domestic cat Felis domesticus allergen I (Fel d I), also referred to as allergen I, cat 1 and antigen 4. Fel d I has been reported to be an acidic non-covalently linked homodimer of approximately 39,000 molecular weight on size exclusion HPLC, and 17,000 under nonreducing conditions on gel electrophoresis. Chapman, M. D., et al. J. Immunology, 140(3):812-818 (1988). Chapman and co-workers also describe a single step procedure for the purification of Fel d I from crude house dust extract with a high Fel d I content (50 U/ml) using monoclonal antibody affinity chromatography. In addition, they report the amino acid composition and partial amino acid sequence of Fel d 1. Fel d I has also been reported to be a 35,000 molecular weight dimer of two noncovalently linked 18,000 molecular weight subunits, which occurs in three isoallergenic forms (pI 3.5 to 4.1). Ohman, J. L., et al., J. Allergy Clin. Immunol., 52:231 (1973); Ohman, J. L., et al., J. Immunol., 113:1668 (1974); Leiterman, K., and Ohman, J. L., J. Allergy Clin. Immunol., 74:147 (1984).
Previous to the present invention, definition or characterization of the structure and components of the Fel d I allergen believed to be responsible for the adverse effects on cat-sensitive individuals was far from complete and current desensitization therapy involves treatment with a complex, ill-defined animal dander extract. However, the presently claimed invention has overcome these deficiencies by providing highly purified and isolated Fel d I (referred to herein as T cell reactive feline protein (TRFP)) free of any other polypeptides and contaminants, as well as identifying those portions of the Fel d I allergen believed to be responsible for causing allergy in cat allergen sensitive individuals. Moreover, the present invention further provides highly characterized therapeutic compositions and methods for treating sensitivity to cats in humans, and which have been further shown to have statistically significant clinical benefit to humans in Phase II clinical trials.